1. Field of the Invention
The present invention relates to novel compounds of neocarzinostatin derivatives having excellent anticancer activity, which have the following formula EQU (SMA)--(NCS)--(SMA) (I)
wherein (NCS) represents divalent neocarzinostatin residue in which one hydrogen atom is removed from each of the primary amino group in alanine residue at the N-terminal of neocarzinostatin and that in lysine residue at 20th position from the N-terminal of neocarzinostatin and (SMA) represents monovalent partially half-esterified styrene-maleic acid copolymeric residue having a weight-average molecular weight of 800.about.2,500 and consisting of structural units of styrene residue ##STR1## half-esterified maleic acid residue ##STR2## wherein R is an alcohol residue wherein hydroxyl group is removed from an alkanol having 1-4 carbon atoms, ethylene glycol monoalkyl ether in which the alkyl group has 1-2 carbon atoms or glycerine dialkyl ether wherein the alkyl group has 1-2 carbon atoms; and maleic acid residue ##STR3## and a residue having the following formula in which a hydroxyl group of one carboxyl group in maleic acid residue is removed and linked to be bonded to the neocarzinostatin residue ##STR4## wherein the linkage of carbon atom in carbonyl group bonds to the neocarzinostatin residue, and a method for producing the same.
2. Description of the Prior Arts
Neocarzinostatin (abbreviated as "NCS" hereinafter) is a proteinaceous anticancer agent produced in a medium in which Streptomyces carzinostaticus var. F-41 Kuroya is cultured (Japanese Patent Publication No. 42 (1967)-21,752 and U.S. Pat. No. 3,334,022). With respect to the primary structure of this substance, the total number of amino acid residues and estimated molecular weight have been reported to be 109 and 10,700 respectively, by Hiroshi Maeda who is one of the present inventors (Science, 178, 875-876 (1972) and Arch. Biochem. Biophys., 163, 379-385).
In the treatment of cancer, the metastasis of cancer cells is important and particularly the metastasis of said cells into lymphatic system is the most important problem. A wide variety of neocarzinostatin derivatives have been examined with the aim of lowering the toxicity, prolonging the biological activity of the drug in vivo, and directing its delivery more to the lymphatic system. As a result, it has been found that neocarzinostatin derivatives having the following formula (II), which is obtained by reacting two primary amino groups present in the molecule of neocarzinostatin with a partially hydrolyzed styrene-maleic anhydride copolymer, possess the above described activities and this has been disclosed in U.S. Pat. No. 4,182,752, EQU (SMA')--(NCS)--(SMA') (II)
wherein (NCS) means the same NCS residue as in the above described formula (I) and (SMA') means styrene maleic acid copolymeric residue having an average molecular weight of 2,500.about.80,000, in which one of the pendant carboxylic groups forms acid amide linkage with a primary amino group in NCS molecule.
But, the above described NCS derivatives are soluble in an aqueous medium and may be applied to intravenous administration but are poor in lipid solubility. The inventors have made various studies for improving the affinity to the tumor by giving both the water and lipid solubility to neocarzinostatin and found that NCS composites shown by the following formula (III) EQU (NCS')--(SMA").sub.n (III)
wherein (NCS') represents NCS residue, (SMA") represents partially half-esterified styrene-maleic acid copolymeric residue having an average molecular weight of 1,000.about.10,000 and the subscript n is an integer of 1.about.35, which are produced by reacting NCS with a partially half-esterified styrene-maleic anhydride copolymer (abbreviated as "E-SMA" hereinafter), have higher affinity to the tumor than NCS derivatives shown by the above described formula (II) and therefore can develop more excellent anticancer activity, and further have excellent water and lipid solubility, so that these NCS composites may be applied in both the forms of the aqueous and the oily compositions and filed with respect to such composites as U.S. patent application Ser. No. 469,235, now pending as Ser. No. 06/730,823, filed May 6, 1985, Canadian Patent Application No. 422,497 and European Patent Application No. 83301027.5.
However, such NCS composites may have a variety of numerical values within a range of n from 1 to 35 but the composites practically produced as the examples have been ones in which the n value is 5 or more. When the biological assay based on the growth inhibition of Sarcina lutea (abbreviated as "biological assay" hereinafter) which has been known to be parallel to the antitumor activity (reported by N. Ishida, K. Miyazaki, K. Kumagai and M. Rikimaru, J. Antibiot (Tokyo), Serial A 18, 68 (1965) is examined with respect to such composites, it has been found that the activity of NCS composites is about 1/10 as compared with that of NCS and said composites are insufficient for the intraarterial administration in which a dose is limited. The reason of such a low biological activity is presumably ascribed to the very high content of the partially half-esterified styrene-maleic acid copolymeric residue to exhibit the biological activity based on NCS residue.